Alternative Photoresist Removal Process to Minimize Damage of Low-k Material Induced by Ash Plasma

Abstract

Dry ashing of photoresist (PR) using oxygen-containing plasma applied subsequently to an etch plasma leads to degradation of porous low-k material. The surface region is substantially depleted in carbon. The low-k film becomes more hydrophilic after being subjected to plasma etch and especially ash process as evidenced by water absorption results. The amount of absorbed water into a 30% porosity film at moisture saturation is estimated to be about 15% of the film volume, which corresponds to 50% of the total pores in the low-k film. A wet, alternative means for PR removal based on dissolution of PR in organic solvents combined with physical forces is presented. Under certain conditions, megasonic cleaning resulted in complete removal of the PR layer without damaging of the dielectric lines. These results suggest that the PR crust is permeable to these solvents and that out-diffusion of dissolved bulk PR also occurred through the crust. Dissolution of bulk PR in organic solvents first makes the PR structure more fragile, then the physical energy helps to remove the remaining crust mechanically without dissolving it. Compared to plasma ashing, solvent strip shows no carbon depletion and no significant increase in k-value.

Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

“…The low-k ILD also provides some mechanical support to metal lines during downstream processing of multiple metal layers and packaging. The low-k DB/CCL/ES, however, serves these and many other additional integrated functionalities such as: preventing Cu out-diffusion into overlying metal layers, 36,37,[72][73][74][75][76] preventing in-diffusion of moisture [77][78][79] and other aqueous cleaning chemicals [80][81][82][83] that can corrode lower metal and ILD layers (see Figure 2), passivating the top surface of the Cu line to reduce/prevent electromigration, [84][85][86][87][88] halting/stopping the trench or via ILD etch to prevent over etching into the underlying metal layer and to facilitate unlanded vias (see Figure 3), 89,90 and prohibiting resist poisoning during next layer metal patterning (see Figure 2). 91,92 As these functionality requirements all relate to the material properties of the DB/CCL/ES, we briefly outline and review the basic electrical, mechanical, thermal and optical material property requirements for these layers in a general nano-electronic metal interconnect.…”

Towards Fully Aqueous Ozone Wet Strip of 193 nm Photoresist Stack Using UV Pre-Treatments in Low-kPatterning Applications

“…In a previous study, we have shown that the cross-linked PR crust is permeable to solvent and that out-diffusion of dissolved bulk PR underneath also occurred through the crust. 7 Apparently the non-crosslinked PR underneath the crust (bulk PR that is not modified by the etch plasma) was removed by dissolution, but not the crosslinked crust PR. 43 In general better removal efficiency was obtained at higher [O 3 ] and higher T, indicating that O 3 dissolved in PC enhanced PR removal.…”

Evaluation of Dielectric Constant through Direct Chemical Mechanical Planarization of Porous Low-k Film

“…10) Thus, improved plasma and/or ashing processes have been well researched and reported. [11][12][13][14][15][16][17] In addition, the uptake of water in nanoporous low-k materials significantly increases the k-values since water molecules have high k-values of $80. 3) The effects of water absorption on the electronic characteristics of LSI devices are reported.…”